It's by far the most explicit verification we've ever had that black holes exist in pretty nearly the exact form predicted by Einstein's equations of general relativity, which is pretty cool. It provides the tightest limits on any possible mass for the graviton (the presumed particle carrying the gravitational force, which is generally believed to be massless but you always have to wonder about more exotic possibilities). It gives a stunningly clear confirmation that modern numerical simulations of relativistic dynamics are an accurate reflection of nature. (And by the same token, it presumably puts limits on the strength of any potential deviation in the laws of physics from the equations used in designing those simulations.) And it probably does something to give preference to models of astrophysics in which binary systems with these characteristics are common.

Beyond that, I guess I'd say that this particular signal doesn't feel like that much of a surprise: we were already pretty confident that if a black hole binary were to merge, a signal more or less like this would be an expected result. The scientists were evidently surprised that their very first signal was so strong (this one was even borderline detectable by the previous version of LIGO), which may teach us something, but it's not revolutionary.

On the webcast, they described how this let us listen in on massive disruptions of space-time, environments we could never create to test on earth, and that could help us better compare our models to events seen in extreme cases.

This is the result the theories predicted, and there's nothing for the theorists to do except gloat. If people had kept building more sensitive detectors, and kept failing to detect gravity waves, then eventually that would have been a very big deal for theoretical physics. But it didn't happen.

On the other hand, there is now a way to see dark matter. That could enable a lot of new astronomy.